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The Tdap vaccine guards against whooping cough as well as tetanus and diphtheria.

The number of whooping cough cases in California has officially reached epidemic proportions, the California Department of Public Health reported.

Whooping cough, known to doctors as pertussis, has experienced a resurgence this year with more than 3,400 new cases reported between Jan. 1 and June 10, according a statement released by the department.

The department said whooping cough is cyclical, peaking every three to five years. The last big spike in cases was in 2010.

Los Angeles County has experienced about 350 new cases so far this year with Long Beach being hit especially hard. The city has seen more than 90 new infections, making up nearly 20 cases per 100,000 people.

Pertussis is a highly infectious bacterial disease that can be spread by coughing. Symptoms of the disease vary by age group.

Adults can find themselves beset with respiratory problems that can last for weeks, while infants who are too young to be vaccinated are in danger of serious illness or death. The common name for the disease comes from the “whooping” sound children can make when experiencing the violent coughing attacks associated with the disease.

Infants may not have typical pertussis symptoms and may have no apparent cough. Parents describe episodes in which the infant’s face turns red or purple.

The organization said two-thirds of pertussis hospitalizations have been in children aged 4 months or younger. Two infant deaths have been reported.

“Preventing severe disease and death in infants is our highest priority,” said Dr. Ron Chapman, director of the department, in the statement. “We urge all pregnant women to get vaccinated. We also urge parents to vaccinate infants as soon as possible.”

The Tdap vaccine, which also guards against tetanus and diphtheria, can be administered to pregnant women to protect infants who are too young to be vaccinated.

In addition, the department said infants should be vaccinated as soon as possible, which can be as early as 6 weeks of age.